1. Evaluation of the impact that moderate hypoxia can have on oyster growth at potential reef restoration sites in Mobile Bay, AL.
Matthew W. Johnson
S. Powers, J. Senne, K. Park
ICSR 2008
Charleston, SC
21 November 2008

2. Oyster Reefs
Oyster “tonging”
Exploitable fishery and an essential habitat for many other species.
Destructive fishing practices remove not only harvestable oysters, but the complicated reef matrix future generation of oysters require.
Hydraulic dredges

3. Point Clear Reefs
Whitehouse
Reef
Fish River/Shell Bank
Cedar Point/Dauphin Island
1407 hectares

4. Oyster Reefs in Alabama
Sub-tidal Reefs
Put and Take Fishery
Unconsolidated
Low relief
Thin veneer
Good for tonging
Photos Courtesy of Mississippi Department of Marine Resources

5. Healthy Oyster Reef Physical and Biological Challenges
Settlement & Growth

7. August 2007
After Katrina
Before Katrina

8. Larval supply Predation Dissolved Oxygen
200
100 10 5 2 1
# spat m-2 d-1
(Hoese et al. 1972)
Predation
Dissolved Oxygen

9. Hypoxia and Restoration
2.5 m
1 m
2 m
1. Stop the reason for hypoxia
2. Build out of the hypoxia
Normoxic
Hypoxic
Anoxic

10. Whitehouse Reef
ADCNR “Reef Donut”
Relic Reef
Mud Bottom

11. Objectives Determine extent of hypoxia in this area.
Ensure that adequate larval settlement to area.
Measure oyster spat survival and growth to see how this related to depth
Short-cut to reef design

12. Design Extreme Hypoxia Moderate Hypoxia No Hypoxia
A priori designation of 3 different oxygen regimes
Similar larvae supply
Similar Depth, m
Control predation
Extreme Hypoxia
Moderate Hypoxia
No Hypoxia
200
100 10 5 2 1

13. 3 replicates per location
Mesh size 1 cm2
3 replicates per location
Oysters deployed on 7/11/2007 and checked biweekly until 9/6/2007, 10/9/2007
Oyster were cleaned of epibionts and counted
Measured at final date
0.5 X 0.5 m
5 X 5 or 4 X 6
79 ± 19 (SD) spat
1.25 m
0.5 m

14. Dissolved Oxygen YSI deployed at each depth at each location
June 29- Aug 27 (5X), Sept 24, Oct 17 Measured DO at 19 stations near Whitehouse Reef

15. Bottom Dissolved Oxygen
1.3 M Off
Whitehouse
Reef

16. Dissolved Oxygen 0-1m (mg l-1)
June 29
July 5
July 19
August 14
August 27
Anoxia
Hypoxia
Normoxia

17. Depth and Growth Location- p<0.001 Depth- NS Time- p<0.001
Repeated Measures ANOVA
Location- p<0.001
Depth- NS
Time- p<0.001
Time x Location p<0.001

18. Theodore Industrial Canal
Whitehouse Reef
Dauphin Island

19. When the hypoxia ends…

20. A B C A B C Height and Length A B 2-way ANOVA
Location x Depth- p<0.001
K-W ANOVA on Ranks
Location- p<0.001
Depth- p<0.001 A B C A B C
2-way ANOVA
Location x Depth- p<0.001
K-W ANOVA on Ranks
Location- p<0.001
Depth- p<0.001 A B C

21. Practical Applications……
> 1.0 m
1.25 m
0.5 m

22. Conclusions Settlement at all depths and all locations
Dissolved oxygen did influence population growth, individual growth
Response under moderate hypoxia similar to that of severe hypoxia

23. Acknoweldgements Funding Personnel
University of South Alabama Oyster Restoration Project
NOAA/NMFS
Personnel
Crystal Hightower
Matt Kenworthy
Jason Herrmann
Stan Bosarge
Multiple Interns

24. Oyster Reefs in Alabama
Decreased long-term production
Stabilized production in recent past

25.
Population in trouble?